Vibration isolation systems are employed in a variety of applications to minimize the transmission of disturbance forces between two bodies or structures. For example, satellites are often equipped with vibration isolation systems to minimize the transmission of vibratory forces emitted from attitude adjustment devices (e.g., control moment gyroscopes or reaction wheel arrays) to other vibration-sensitive components (e.g., optical payloads) carried by the satellite. The performance of a vibration isolation system is largely determined by the number of isolators included within the system, the manner in which the isolators are arranged, and the vibration attenuation characteristics of each individual isolator. Vibration isolation systems employing three parameter isolators, which behave mechanically as a primary spring in parallel with a series-coupled secondary spring and damper, provide superior attenuation of high frequency vibratory forces as compared to vibration isolation systems employing other types of passive isolators, such as viscoelastic dampers. An example of a three parameter isolator is the D-STRUT® isolator developed and commercially marketed by Honeywell, Inc., currently headquartered in Morristown, N.J. Such isolators are often passive, single Degree of Freedom (DOF), axially-damping devices well-suited for usage within multi-point mounting arrangements.
While providing the above-noted advantages, three parameter isolators remain limited in certain respects. Three parameter isolators are typically passive devices and, as such, generally cannot be tuned to provide broadband damping across a wide frequency range. This can be disadvantageous as multiple critical modes can exist over a broad frequency range and can vary over time with changing loads, imbalances, bearing imperfections, and the like. Similarly, the dynamic stiffness of a passive three parameter isolator is typically fixed by isolator design and by the viscosity of the selected damping fluid. By common design, three parameter isolators also include a sealed-bellows damper containing damping fluid, which can further limit isolator capabilities in a number of respects. The damping fluid can, for example, restrict the overall temperature capabilities of three parameter isolator, which may be undesirable when the isolator is utilized within an extremely hot or extremely cold (e.g., cryogenic) environment. While damping fluid temperature can be regulated through the usage of heaters and/or cooling circuits, this adds undesired cost, weight, and bulk to the isolator. Additionally, in applications wherein the isolator operates over a relatively broad temperature range, damping fluid viscosity changes can negatively impact isolator performance. A thermal compensation system can be utilized to maintain acceptable fluid operating pressures despite thermally-induced changes in damping fluid volume; however, this again adds undesired cost, weight, and bulk to the isolator. Finally, in the unlikely event of fluid leakage, the damping fluid can potentially contaminate sensitive equipment, such as optical sensors, positioned near the isolator.
It is thus desirable to provide embodiments of a vibration isolation system including multi-parameter isolators, which provide damping performance comparable to that provided by passive three parameter isolators, while also overcoming one or more of the limitations described above. It would be particularly desirable to provide embodiments of a vibration isolation system capable of actively adjusting its damping capabilities to, for example, target critical modes as they change over time and/or to provide different operational modes. It would also be desirable for such a vibration isolation system to overcome the above-noted drawbacks associated with fluid dampers to, for example, enable operation of the vibration isolation system at highly elevated or highly depressed (e.g., cryogenic) temperatures. Other desirable features and characteristics of embodiments of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying drawings and the foregoing Background.